Your pathology report for endometrioid carcinoma of the ovary

by Jason Wasserman MD PhD FRCPC
August 23, 2025

Endometrioid carcinoma is a type of ovarian cancer that starts from the epithelial cells, which are the cells that normally cover the surface of the ovary and line the glands inside the uterus. It accounts for about 10% of all ovarian cancers.

Many cases of ovarian endometrioid carcinoma are associated with a condition called endometriosis. Endometriosis occurs when tissue that normally lines the inside of the uterus (the endometrium) is found outside of the uterus. The ovary is one of the most common locations for endometriosis, and in a small percentage of people with endometriosis (about 1%), a tumour such as endometrioid carcinoma may develop.

Similar tumours can also occur in the uterus. In fact, sometimes ovarian and uterine endometrioid carcinomas are found in the same patient.

What are the symptoms of endometrioid carcinoma of the ovary?

The symptoms of ovarian endometrioid carcinoma are often vague and can be mistaken for other conditions. Common symptoms include bloating, abdominal or pelvic pain, changes in bowel or bladder habits, feeling full quickly when eating, and abnormal vaginal bleeding. Some patients may also notice a lump or mass in the lower abdomen. Because the symptoms are nonspecific, the disease is often diagnosed at a later stage.

What causes endometrioid carcinoma of the ovary?

Most cases of endometrioid carcinoma (about 85 to 90%) develop from endometriosis. In these cases, the tumour and the endometriosis tissue often share the same genetic mutations, showing that the cancer arose from the endometriosis.

A smaller number of tumours develop from other benign or borderline growths of the ovary, such as endometrioid adenofibromas. In addition, up to one quarter of patients will have a second tumour at the same time, either an endometrioid carcinoma or a precancerous condition in the uterus.

What are the subtypes of endometrioid carcinoma of the ovary?

Doctors have identified four molecular subtypes of endometrioid carcinoma of the ovary. These subtypes are based on specific genetic changes seen in the tumour cells.

• Hypermutated tumours: These tumours develop because of a problem with the DNA repair system called mismatch repair. About 13% of ovarian endometrioid carcinomas fall into this group.

• Ultramutated tumours: These tumours have mutations in a gene called POLE. This change leads to a very high number of mutations in the tumour cells. About 5% of ovarian endometrioid carcinomas belong to this group.

• TP53-mutated tumours: These tumours have changes in a gene called TP53, which normally helps control cell growth and repair DNA damage. About 9 to 13% of cases fall into this category.

• No specific molecular profile (NSMP): This is the largest group, accounting for about 70% of ovarian endometrioid carcinomas. These tumours do not show the distinct genetic patterns seen in the other subtypes.

Other genetic changes are also common in these tumours. Many show changes in the WNT/β-catenin pathway (CTNNB1), the PI3K pathway (PIK3CA and PTEN), the MAPK pathway (KRAS), and in genes such as ARID1A that help control how DNA is packaged and used by the cell. These molecular changes may eventually be used to guide treatment.

How is this diagnosis

The diagnosis is usually made after the tumour has been surgically removed and examined by a pathologist under the microscope. Sometimes, a small piece of the tumour may be sampled with a biopsy, but most cases are diagnosed after surgery.

What is an intraoperative consultation (frozen section)?

During surgery, your surgeon may ask a pathologist to examine the tumour right away to help guide treatment. This is called an intraoperative consultation. A frozen section may be performed, which involves quickly freezing a piece of tissue so it can be examined under the microscope. The pathologist provides a rapid preliminary diagnosis that helps the surgeon decide how much tissue should be removed. The final diagnosis is always made after the tissue is processed more carefully after surgery.

How do pathologists determine the FIGO grade?

Pathologists divide endometrioid carcinoma of the ovary into three grades based on how the tumour cells grow:

• Grade 1: Most of the tumour forms round structures called glands, and very little of the tumour shows a solid growth pattern.

• Grade 2: The tumour forms some glands but also shows areas of solid growth.

• Grade 3: Very few glands are present, and most of the tumour grows in a solid pattern.

If most of the tumour cells also have very abnormal-looking nuclei (the part of the cell that holds genetic material), the grade is increased by one level. Pathologists call this severe nuclear atypia.

The FIGO grade is important because it predicts how the tumour is likely to behave. Grade 1 tumours tend to grow more slowly, while grade 3 tumours behave more aggressively and are more likely to spread.

Were tumour cells seen on the surface of the ovary or fallopian tube?

Tumour cells can sometimes spread to the surface of nearby structures such as the ovary or fallopian tube. If this is seen, it means the tumour has already begun to spread outside of its original location. This finding increases the tumour stage (T stage) and usually indicates a higher risk that the tumour could come back after treatment.

Why is it important if the tumour was received intact or ruptured?

The outer layer of the ovary is called the capsule. If the capsule is intact, the tumour was contained within the ovary. If the capsule is ruptured, tumour cells may spill into the abdominal cavity, increasing the risk of spread. Rupture can happen before surgery or during surgery, and sometimes it may not be possible for the pathologist to tell when it occurred. A ruptured capsule is associated with a worse prognosis and is used to assign a higher stage.

Has the tumour spread to other organs or tissues in the pelvis or abdomen?

Small tissue samples, called biopsies, are often taken during surgery to check if the tumour has spread outside of the ovary. These biopsies are commonly taken from the lining of the abdomen, called the peritoneum. Another common site is the omentum, a fatty tissue in the abdomen where ovarian cancers often spread.

Sometimes, the tumour grows directly into nearby organs such as the bladder or intestines. If this occurs, the pathologist will examine those tissues carefully under the microscope. The presence of tumour cells in these sites is important for determining both the tumour stage (T stage) and whether there is distant metastatic disease (M stage).

Were lymph nodes examined and did any contain cancer cells?

Lymph nodes are small immune organs located throughout the body. Cancer cells can travel to lymph nodes through lymphatic vessels. For this reason, lymph nodes are often removed and examined.

Your pathology report will include the total number of lymph nodes examined, the number that contained cancer cells, and the size of the largest group of cancer cells. This information is used to determine the nodal stage (pN). Finding cancer cells in lymph nodes increases the risk of the cancer spreading further and helps guide decisions about additional treatment.

• Positive lymph node: A lymph node that contains cancer cells.

• Negative lymph node: A lymph node that does not contain cancer cells.

• Isolated tumour cells (ITCs): Very small groups of cells measuring 0.2 mm or less. These are not counted as positive when determining nodal stage.

• Micrometastasis: A small group of cancer cells between 0.2 mm and 2 mm in size.

• Macrometastasis: A larger group of cancer cells more than 2 mm in size.

• Extranodal extension: Cancer cells breaking through the capsule of the lymph node into surrounding tissue. This is associated with a higher risk of the tumour growing back and may be a reason to consider additional treatment.

What is mismatch repair testing and why is it performed?

Cells in our body have systems to repair damage to DNA, which is the set of instructions that controls how cells grow and function. One of these systems is called the mismatch repair system. It is made up of four main proteins: MLH1, PMS2, MSH2, and MSH6.

If any of these proteins stop working, DNA damage can build up inside the cell, eventually leading to cancer. Pathologists can test for mismatch repair deficiency in tumours by looking to see if the proteins are present.

Most cases of mismatch repair deficiency in ovarian endometrioid carcinoma are not inherited but occur only in the tumour. However, in a small number of cases, the deficiency is inherited. This is called Lynch syndrome, a genetic condition that increases the risk of several cancers including ovarian, colon, and uterine cancer.

If mismatch repair deficiency is found in your tumour, your doctor may recommend further genetic testing to determine whether you have Lynch syndrome. This information is important not only for you but also for your family members, who may also be at risk.

How do doctors stage ovarian cancer?

Staging is a way of describing how far a cancer has spread in the body. For ovarian cancer, two main systems are used: the TNM system and the FIGO system. Both are internationally accepted and provide important information about prognosis (the expected outcome) and treatment planning.

The TNM system

The TNM system is developed by the American Joint Committee on Cancer (AJCC). It looks at three main factors:

• T (tumour): Describes the size of the tumour and how far it has spread in or around the ovary or fallopian tube.

• N (lymph nodes): Describes whether cancer cells have spread to nearby lymph nodes.

• M (metastasis): Describes whether cancer has spread to distant parts of the body.

Breakdown of the T stage:

• T1: The tumour is limited to one or both ovaries or fallopian tubes.

  • T1a: Tumour is inside one ovary or fallopian tube, with the outer surface intact and no cancer cells in fluid taken from the abdomen.

  • T1b: Tumour is inside both ovaries or fallopian tubes, but the outer surfaces are intact and no cancer cells are found in fluid.

  • T1c: The tumour is limited to one or both ovaries or tubes, but there has been a rupture, tumour on the outer surface, or cancer cells found in abdominal fluid.

• T2: The tumour has grown into tissues in the pelvis, such as the uterus or bladder.

  • T2a: Spread to the uterus or other fallopian tube or ovary.

  • T2b: Spread to other pelvic tissues.

• T3: The tumour has spread beyond the pelvis into the abdomen or to regional lymph nodes.

  • T3a: Cancer cells are found microscopically outside the pelvis or in nearby lymph nodes.

  • T3b: Visible tumour deposits up to 2 cm outside the pelvis or in nearby lymph nodes.

  • T3c: Visible tumour deposits larger than 2 cm outside the pelvis or involving the capsule of the liver or spleen (without entering the organ itself).

Breakdown of the N stage:

• N0: No cancer cells are seen in regional lymph nodes.

• N0(i+): Only isolated tumour cells smaller than 0.2 mm are seen in the lymph nodes.

• N1: Cancer cells are found in regional lymph nodes.

  • N1a: Deposits up to 10 mm.

  • N1b: Deposits larger than 10 mm.

The FIGO system

The FIGO (International Federation of Gynecology and Obstetrics) system is specifically designed for gynecologic cancers like ovarian cancer. It uses similar criteria to the TNM system but is grouped into broader stages that are easier to interpret clinically.

Breakdown of FIGO stages:

• Stage I: Cancer is limited to the ovaries or fallopian tubes.

  • IA: In one ovary or fallopian tube only.

  • IB: In both ovaries or fallopian tubes.

  • IC: Cancer is still limited to the ovaries or tubes but there has been a rupture, tumour on the surface, or cancer cells found in fluid.

• Stage II: Cancer involves one or both ovaries or tubes with spread to pelvic organs such as the uterus, bladder, or rectum.

  • IIA: Spread to the uterus or other ovary/tube.

  • IIB: Spread to other pelvic tissues.

• Stage III: Cancer has spread outside the pelvis into the abdominal cavity or to regional lymph nodes.

  • IIIA1: Cancer in lymph nodes only.

  • IIIA2: Microscopic spread outside the pelvis.

  • IIIB: Visible spread outside the pelvis up to 2 cm.

  • IIIC: Visible spread larger than 2 cm or spread to the capsule of the liver or spleen.

• Stage IV: Cancer has spread to distant organs outside the abdomen.

  • IVA: Cancer cells are found in the fluid around the lungs.

  • IVB: Cancer has spread to organs such as the liver, spleen, or lymph nodes outside the abdomen.

Why staging matters

Both TNM and FIGO staging systems provide doctors with essential information about how far the cancer has spread. This helps guide treatment choices, such as whether surgery alone is enough or if chemotherapy or other treatments are needed.

Staging also helps predict prognosis. Early-stage disease (stage I) has a much better survival rate compared to advanced-stage disease (stage III or IV). By using staging information, doctors can personalize care and discuss treatment options and expectations with patients.

Prognosis for endometrioid carcinoma of the ovary

The most important factor in prognosis is the stage of the tumour at the time of diagnosis. Most tumours are found at an early stage (stage I), when they are still confined to the ovary. In these cases, the prognosis is excellent, with more than 95% of patients surviving at least 5 years. The survival rate decreases if the tumour is diagnosed at a later stage, with about 89% survival for stage IC/II and about 51% for stage III/IV.

Other features can also affect prognosis. For example, tumours with squamous differentiation (where the tumour cells look like squamous cells) are usually low grade and linked to better outcomes. Some tumours are tested for molecular markers, and changes in genes such as POLE, CTNNB1, and TP53 can help predict behaviour.

In rare cases, patients may have tumours in both the ovary and the uterus at the same time. Research shows that these are often related to each other, but they usually behave less aggressively than widespread metastatic disease. If both tumours are low grade, confined to their original sites, and do not show extensive invasion, doctors may treat them as separate tumours rather than one tumour that has spread.

Questions to ask your doctor

If you have been diagnosed with endometrioid carcinoma of the ovary, you may wish to ask your doctor the following questions:

• What grade is my tumour, and what does that mean for my prognosis?

• Was the capsule of the ovary intact or ruptured?

• Did the cancer spread to other organs or tissues in the pelvis or abdomen?

• Were lymph nodes examined, and if so, did they contain cancer cells?

• Has my tumour been tested for mismatch repair deficiency?

• Should I or my family members be tested for Lynch syndrome?

• What stage is my cancer, and how does that affect treatment options?

• What are the recommended treatments for me, and what side effects should I expect?